1. Field of the Invention
The present invention relates to a constant-mesh transmission, such as a gear-type transmission mounted on a vehicle.
2. Description of Background Art
As a transmission of this type, for example, a constant-mesh transmission disclosed in Japanese Patent Publication No. Hei-2-39660, is known. A transmission 01 has, as shown in FIGS. 9 and 10, a transmission gear 03 formed integrally with a main shaft 02, and a transmission gear 05 which meshes with the gear 03 and is rotably provided for a counter shaft 04. In the transmission gear 05, a recess 07 is formed having a bottom in which a plurality of nails 06 are formed at intervals in the circumferential direction. A synchronizer ring 08 constructing a synchronizing mechanism in teamwork with the recess 07 is assembled in the recess 07 so as to be relative to the transmission gear 05. In the synchronizer ring 08, a plurality of openings 09 are formed at intervals in the circumferential direction, and an arm 010 having a chamfer 011 is formed between two neighboring openings 09. In a transmission gear 013 (slider) provided for the counter shaft 04 so as to be slidable in the axial direction and moved by a shift fork 012, nails 014 are formed at intervals in the circumferential direction, which can be inserted into the openings 09.
As shown in FIG. 10(A), at the time of changing speed, the transmission gear 013 moved by the shift fork 012 moves the synchronizer ring 08 via a synchronizer spring 015 from a speed change start position, thereby allowing a tapered face 016 of the synchronizer ring 08 to come into contact with a tapered face 017 of the second gear 05, and thus generating a frictional torque. This causes a chamfer 018 of the nail 014 and the chamfer 011 of the arm 010 to come into contact with each other. When the transmission gear 013 further presses the synchronizer ring 08, the transmission gears 013 and 05 are synchronized with each other via the synchronizer, ring 08, with a high frictional torque generated on both the tapered faces 016 and 017.
As shown in FIG. 10(B), after completion of synchronization of both of the gears 013 and 05, the transmission gear 013 is further moved in the axial direction, the nails 014 mesh with the nails 06 formed on the bottom of the recess 07, and the speed changing operation is completed.
In the conventional technique, the nails 014 of the transmission gear 013 as a slider moves in the axial direction. First, nails 014 come into contact with the chamfers 011 of the arms 010 with respect to the arms 010 and nails 06 positioned in a straight line in the axial direction and are inserted into the openings 09. Subsequently, nails 014 mesh with the nails 06 of the transmission gear 05. Therefore, a movement stroke LO in the axial direction of the transmission gear 013 from the speed change start position to the speed change completion position is long. This is one of the factors causing an increase in the size in the axial direction of the transmission 01. In the case of shortening the movement stroke LO, the width in the axial direction of the arm 010 having the chamfer 011 is narrowed, so that it becomes difficult to assure sufficient rigidity of the arms 010 of the synchronizer ring 08 pressed in the axial direction by the nails 014.
It is an object of the present invention to realize minimization in the axial direction of a constant-mesh transmission having a synchronizing mechanism and to achieve high rigidity of a synchronization spline formed in a synchronizer ring. Another object of the invention is to prevent an increase in size of the radial direction of a synchronizing mechanism.
The invention is directed to a constant-mesh transmission comprising a first gear provided for a first rotary shaft as to rotate integrally with the first rotary shaft, a second gear which meshes with the first gear and is rotatably provided for a second rotary shaft, and a synchronizing mechanism. The synchronizing mechanism includes a shifter provided for the second rotary shaft so as to rotate integrally with the second rotary shaft and to be movable in the axial direction, ring-shaped recess formed in the first gear, and a synchronizer ring disposed in the recess so as to be rotatable relative to the second gear and pressed by the shifter at the time of changing speed to move in the axial direction so as to come into frictional engagement with the first gear, thereby achieving synchronization between the shifter and the first gear.
In turn, the shifter include a first connection spline formed in a circumferential wall face of the recess and a first synchronization spline formed in a circumferential face of the synchronizer ring occupying a position where they at least partly overlap with each other in the axial direction. The shifter also includes a second connection spline which can mesh with the first connection spline and a second synchronization spline which presses the first synchronization spline in the axial direction to make the synchronizer ring and the first gear come into frictional engagement with each other, and can mesh with the first synchronization spline. At the time of changing speed, the first and second synchronization splines mesh with each other, after which the first and second connection splines mesh with each other.
According to the present invention, at the time of changing speed, the second synchronization spline of the shifter presses the first synchronization spline of the synchronizer ring, the synchronizer ring is moved in the axial direction and comes into frictional engagement with the first gear, thereby achieving synchronization between the shifter and the first gear. After completion of the synchronization, the first and second synchronization splines mesh with each other, and then the first and second connection splines mesh with each other, whereby the speed changing operation is completed.
As a result, the following effect is produced: Specifically, the first connection spline and the first synchronization spline have an overlap portion where they overlap with each other at least partly in the axial direction. Consequently, the movement distance of the shifter until completion of the sped changing operation is minimized, since the synchronizer ring is moved in the axial direction by the shifter, and the synchronizer ring and the first gear come into frictional engagement with each other to achieve synchronization between the shifter and the first gear. Then, after completion of the synchronization, the first and second synchronization splines mesh with each other. Finally, the first and second connection splines mesh with each other. With the configuration of the present invention, the movement stroke becomes shorter than with conventional configurations. It becomes possible to reduce the width in the axial direction of the first gear in which the recess is formed and dispose the first gear and the shifter so as to be closer to each other in the axial direction. Thus, the size of the transmission can be reduced in the axial direction.
Moreover, the first synchronization spline pressed by the second synchronization spline occupies a position where it overlaps with the first connection spline at least partly in the axial direction. As compared with the case where the first synchronization spline and the first connection spline are positioned without being overlapped in the axial direction, the width in the axial direction of he first synchronization spline can be increased and the rigidity of the first synchronization n spline against the pressing force acting from the second synchronization spline can be increased. This can be accomplished without increasing the width in the axial direction of the recess in which the synchronizer ring is disposed, and without increasing the width in the axial direction of the first gear in which the recess is formed.
According to another aspect of the present invention, a ring-side tapered portion is formed on the side opposite to the shifter in the axial direction for the first synchronization spine in the circumferential face of the synchronizer ring, and a gear-side tapered portion, with which the ring-side tapered portion comes into frictional engagement at the time of changing speed, is formed in a circumferential wall face of the recess.
With this feature, the following effect is produced: Specifically, in the synchronizer ring, the tapered portion is provided on the side opposite to the side where the shifter is positioned in the axial direction for the first synchronization spline. Thus, the first synchronization spline and the tapered portion are not parallel to each other in the axial direction, which otherwise would enlarge the synchronizing mechanism in the radial direction. Accordingly, the synchronizing mechanism having diameter can be assembled in a transmission gear.
In the specification, xe2x80x9caxial directionxe2x80x9d denotes a direction of rotation axis line of a rotary shaft of a constant-mesh transmission, and xe2x80x9cradial directionxe2x80x9d denotes a radial direction when the rotation axis line of the rotary shaft is used as a center.
Further scope of applicability of the present invention will become apparent detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.